Chrysotile asbestos is a fibrous silicate used commonly in a number of manufacturing processes. This serpentine mineral is composed primarily of magnesium (Mg) hydroxide and silicon (Si) dioxide (Mg6(OH)8Si4O10). Magnesium ions are readily translocated from chrysotile fibers in a variety of media (e.g. saline at body temperature, organic and inorganic acids) and in human lungs. The toxicity of magnesium-leached fibers seems to be altered under certain experimental conditions. We are investigating in vitro and in vivo systems in which the elemental content of chrysotile asbestos can be critically evaluated and correlations with cytotoxic events can be made. Treatment of aliquots of chrysotile asbestos with NHCL causes a slow translocation of Mg ions so that the ratio of Mg to Si changes from control level of .71 to .49 after 8 hours. Such changes do not occur after aldehyde fixation or plastic and paraffin embedding. Inhaled chrysotile asbestos in the lungs of rats showed clear changes in elemental ratio.